Solar cells use the characteristics of semiconductors to convert solar light into electric energy. The solar cells receive attention as an alternative energy source which can substitute for existing energy sources, such as petroleum, coal, etc., because the solar light is abundant and does not cause environmental pollution.
Such a solar cell is the minimum unit which uses solar light to generate electricity. Photovoltaic modules include a plurality of solar cells which are connected in series to each other to produce the appropriate voltage and current. Such a photovoltaic module is manufactured in such a way that after solar cells are connected in series, they along with a filler, glass, etc. are pressed to be protected from the external environment. The photovoltaic module is installed to be oriented towards the southern sky in the northern hemisphere to increase the amount of solar light it receives.
However, the energy conversion efficiency of the solar cells ranges between 10% and 20%. The reason that the energy conversion efficiency is comparatively low is that the solar cells can convert only some of the received solar light into electric energy. The light energy that has not been converted into the electric energy is converted into thermal energy (the energy loss attributable to this is 60% of the entire energy loss), thus increasing the temperature of the photovoltaic module.
Due to the characteristics of the solar cells, the output of power of the photovoltaic module is reduced by an increase in temperature. If the generating efficiency is 100% at 25° C., the output of power is reduced by 0.45% to 0.55% every increase in the temperature of 1° C.
That is, in the solar cells, the temperature is inversely proportional to the output voltage. Hence, as the temperature increases, the output voltage is reduced, thus reducing the generating output of power. As a result, in the hot summer, the power output generation is low, considering the amount of solar radiation.
Further, the increase in temperature causes deterioration of the solar cells. Thus, the power output generation becomes less over time.
To prevent these problems, a method of planting grass or spacing solar cells apart from each other to cool them in an air-cooling manner has been used, but the effect of a reduction in temperature is insignificant.
In addition, a forced cooling technique using equipment such as a cooling fan or the like may be used to cool the solar cells. This requires electricity, incurring additional costs. Moreover, additional labor is required to manage and maintain the equipment. Therefore, the effect which can be obtained by reducing the temperature becomes very low, considering the required expenses. Thus, this technique cannot be actualized.